Rear cog skipping

[H12rpo]

Specialised rockhopper
I’m familiar with the outer and inner limiting screw adjustment and that’s fine. The indexing works fine and the jockey wheels are aligned with the cogs. What I’m getting though is that sometimes (mostly when under stress) the chain skips between 3 and 4 cog as if it can’t make up it mind. What do I adjust to stop that? It’s really beginning to cheese me off

 

[ColinJ]

Is the cassette significantly worn?

 

[H12rpo]

Nope it’s only 5 months old

 

[gilespargiter]

Difficult one - everything apparently perfect, but it don't work!

Check for chain wear. If this is good, check that the chain fits round the cassette sprockets properly. If it skips between two sprockets, as distinct from skipping round them - then the indexing is not working properly - has it the correct number of sprockets? If you can, see what happens if you set it on friction shifting. If it is running round then either or both the cassette and chain are worn (or the chain has "stiff" links - rust or damage). In this case both will need replacing.

FYI. I have found that I can completely trash a chainset in less than a year if I traverse the N.Wales cycleway when the wind is blowing sand on shore at all often.

 

[gilespargiter]

Worth drawing your attention to this thread perhaps; https://www.cyclechat.net/threads/what-am-i-doing-to-cause-my-rear-gears-to-slip.240726/page-2

 

[screenman]

Read mech alignment, you cannot check by eye.

 

[I like Skol]

Might be worth backing off the cable tension slightly. There is a small amount of tolerance in the indexing precision due to the floating top jockey wheel and chain/cassette clearances and in the past I have found it is better to be at the slacker end of that tolerance. This effectively means tightening the cable tension just enough to get a good shift to a larger sprocket, rather than the alternative which is loosening the cable just enough to get the drop to a smaller sprocket.

 

[the snail]

Apart from tensioning cable and hanger alignment as mentioned, stickiness/dirt in cables and derailleur pivots possibly. The outer by the RD is very prone to getting clogged.

 

[si_c]

If the chain is skipping side to side then the system is not correctly indexed. This is most likely cable tension (adjust it about a 1/4 turn as per @I like Skol), but it could also be the rear wheel not seated properly if a QR wheel or the derailleur hanger isn't straight.

To adjust the cable tension on shimano gears, if it's going UP the cassette (moving to the left) then turn the derailleur clockwise, if it goes down the cassette then turn it anticlockwise. The idea being to get the gearing to settle on one gear, with the presumption that the gear you want it in being the one that it jumps away from. Just turn it a quarter turn at each time, once it stops moving, turn it once more, but only about 1/8th of a turn.

 

[User6179]

If it skips when you are going down the cogs and not when going up then it is usually the cable sticking.

Could also be a wobbly hub, pick up the bike and spin the pedals, hold the bike secure and watch the cassette to see if it is wobbling about on the hub

 

[H12rpo]

Thanks for the tips fellas. I think it may well be cable tension.
There’s another screw though that adjusts the closeness of the uppermost jockey wheel nearer to the cassette or further down/ away from it......whats the ideal distance ? And does that affect the cog skipping probability?

 

[gilespargiter]

^^ The "B" scew - it won't affect it skipping. If it changes across the cassette it is very unlikely to bo wrong.

 

[Nigelnightmare]

IIRC The ideal distance is 6mm but as long as it's about the same in top and bottom gear.
Is the new cassette the same make as the old one?

Spacing on new cassette may be different!

 

[H12rpo]

I haven’t got a new cassette. It’s the original one and chain. They’re not worn and i havent done that many miles. Thanks for the tips though guys I’ll try adjusting the cable a bit at a time.